If you punch in the specs, it spit this out for 155/70 r19, and 175/60 r19(REX)
tires:
For comparison this is the 115/80 r15 and 145/55 r16 of the XL1.
And the Xl1's 115/80 r15 compared to the Insights 165/65 r14:
IT would only be 0.2 inches smaller for a 0.9% difference. 0.6inches less sidewall, and the magic number:
43.5% less width!
If you look through European websites 155/70 r19 spare tires are actually a standard size. You can buy these tires fitted for spares. They're for various luxury cars that run 19inch wheels. The problem is the spares are usually bulged outward to clear large brakes. May or may not be ideal. 19inch spares are always some 5 bolt pattern.
You can get 115/80 r15 spares from Mini coopers with 4x100 bolt patterns in the US same as stock Insight wheels. These are ideal if i could get some XL1 tires. The Xl1 is a 4 bolt wheel. I would wish it was 4x100. 4x100 was actually a standard bolt pattern on older VW's. But 4x115 is also common on other vehicles so who knows. The XL1 wheels are made of gloriously expensive Magnesium unobtainium though!
If you couldn't somehow change the bolt pattern, Wheel adapters might work. All the forums and websites say not to use them though. I think last i recall a set of four factory i3 wheels are at least more than $1,150. Probably more.
I searched this thread, and a while back i said the BMW i3 had a 5 x 114.3 bolt pattern. I can't confirm if that is true or not. Neil had a post on his Facebook page several months back all about the i3 wheels and tires, including prices and bolt pattern. I'm not able to find it though.